View Full Version : Feasible to skim a cylinder head on a mill?
I would like to skim 50thou from the cylinder head of a 1275 MG Midget motor (going into my Morris Minor). How is this done in a machine shop? On a surface grinder? Could I skim it using a flycutter on my mill? (Asssume I have the skill - which I probably don't!).
My mill is man enough for it - 10x51 table with power feed, but is it a good idea?
11-19-2003, 11:46 PM
If you have a large enough face mill to cover the whole surface it will work fine.that's asicly what my machine does,it just uses dedicated fixtures to speed the mounting process.
11-20-2003, 12:12 AM
You might be better off taking .125" off of the 1275 head. Then you can use a reground 731 or MM-55 cam and the smaller base circle will compensate for the "shave". I little compression really wake a 1275 up.
11-20-2003, 12:18 AM
There was an article in either HSM or MW about doing just that. Steve Chastain gave a step by step that made it look very do-able
It was earlier this year, but can't remember which month.
11-20-2003, 12:50 AM
Ken: I know nothing about that particular engine,but milling a head is BETTER than grinding (I never heard of grinding one).
The milling leaves just enough "tooth" to grip the head gasket and keeps blown head gaskets down. Some say keep the millhead vertical. I like just a little tilt.
GA: I don't have a face mill that size, I suppose they cost a fortune to buy right?
Jason: .125? Assuming the same valve lift as stock any problem with valves and pistons clashing?
Sprocket: Typical! I have HSM from 83-2002!
Doc: Thanks, that's what I wanted to know, just didn't have any idea if a mill would be adequate.
Thanks to all!
11-20-2003, 01:25 AM
Not sure how big of a face mill you'd need, but likely it will be spendy (unless ebay can save you).
But why not use a good rigid flycutter?
He he, I suppose that will make it a Morris Major... Burn that rubber! Except it will probably take the lead (Pb) teeth right off of first gear.
[This message has been edited by Evan (edited 11-20-2003).]
Oh yeh.... ;-)
It's going to kick butt.
Let's see, 73 Midget engine with the low compression pistons, using (at least for now) the masssive 1-1/4" single SU on the worlds most inefficient intake and exhaust manifold. It should put out about 60hp if I'm lucky!
The original 1098 in/ex manifold fits which helps get things going.
The pistons are in good shape so I figured I'd reuse them (with new rings) but I'd skim the head to get maybe a half a point of CR back from the LC pistons.
Later I intend fabricating a long center branch" header and a decent intake manifold for the twin 1-1/2" SU's I've got stashed away.
With a bit of porting, I reckon after all of that I'll be up to 61.5hp and will be dicing it out with Yugos!
Hey, just had a thought. Since it's a 73 motor and has the LC pistons that probably means it was set up for unleaded - maybe it has hardened valve seats?
That would be handy........
11-20-2003, 07:35 AM
When I was an idiot apprentice, a guy in the Hard Chrome dept. gave me a Dodge flathead six head to mill. I set it up on a Bridgeport with a 3" multi tip carbide cutter - it was no fun, and after roughing it down, I gave it back to him and told him to get it finished by an automotive reconditioner.
I wouldn't muck about with this job, engine rebuilders will do it right for not a big cost.
11-20-2003, 08:47 AM
A head can either be milled or ground. The imporant thing is the resulting finish quality. You want to end up with an RA (degree of roughness) that matches the requirements of the head gasket. „h Milling machines can consistently provide any desired surface finish, even as low as 12 RAs.
+ Most gasket manufactures recommend a surface RA of 54 - 113
+ The preferred RA range is 20 ¡V 60
+ The new laminated steel gaskets require a finish less than an RA of 20 with a maximum RA of 30.
Don't listen to someone who hasn't worked with this for a number of years as thier knowledge will be out-of-date. Check with your gasket mfg for their RA recommendation.
I don't know if you really need to worry about unleaded gas. It is supposed to cause some valve erosion due to poor lubricating properties vs tetra ethyl lead but I have been running unleaded in my Land Rover since the late '70s with no apparent problems. It has never been converted or fiddled with in any way and I have no valve problems. It is a very low compression engine, about 7.5 to 1.
11-20-2003, 03:47 PM
With unleaded gas, and unhardened valve seats, eventually the valves will recede into the head and the engine will cease to run. It is usually not noticeable until the seats are gone, especially on low performance engines. Hardened inserts are available.
Must not be happening on the Land Rover as I haven't needed to adjust the tappets in many years. That engine starts on the first crank down to about zero, then I have to plug it in.
Check out Steve Chastain's article in the July/Aug 2003 HSM.
11-20-2003, 07:05 PM
ASALLWEY is right about finish and up to date knowledge.
I stand by my info on OLDER heads. On multilayer, steel gaskets the needs are considerably different.
A free trade magazine "Precision engine" (formerly "Precision Machine shop") has several articles on head gaskets. If you run across a stack of the magazines try to get them. I suspect they are going belly up, because they publish erratically now.
Anyway, Fel-Pro wrote one article for them and says they (fel pro) find more failures due to too smooth heads than any other cause. Fel -Pro says you should almost be able to "snag" a finger nail on a well machined head. Of course, follow the gasket makers instruction in all cases, but for old gaskets-leave them with "tooth" in absence of other information. And torque in steps, three or more, and re torque after use if at all possible.
In the case of re-torque, I feel re-torque even is worth while even when the instructions say no need- but you pays your money and takes your chances rather you follow instructions or not.
11-20-2003, 10:20 PM
I don't know how a flycutter would do.Keep in mind the interupted cuts,plus the length of the part,then add in cast irons grittyness that will dull a high speed tool before it gets halfway through the job.(Automotive machines have been using carbide since the 50's).
As for a large enough face mill,look on eBay as AmickRacing suggested.
Then again,as others have noted,an automotive shop could be your best bet.
Grinding was a common practice on cast iron.It is somewhat outdated now.I have an older head grinder that is out of service that I'm planning on converting to cbn cutters.
Grinding won't work very well on aluminum.That is the primary reason that it has fallen out of favor.That and it is so sloooow.(And so messy).
About Precision Machinist:
It's now Precision Engine.They do publish infrequently.I think they publish one when they have a big company to promote (read be sponsored by). http://bbs.homeshopmachinist.net//smile.gif
The engine in those old Land Rovers were built to last and run on whatever fuel could be found where ever the were in the world.
They probably had hardend valve seats in them from the factory.
Asallway's advice is right on the mark.
I helped a guy build a Midget engine (same thing + or-) a few years ago.
We offset bored it to 74.7 mm.I don't recall how much the final dispalcement was,but it was a large increase.
He had a book on hotrodding them that we went by.It appears that they are really popular to race in the UK.
11-20-2003, 10:49 PM
I let the pros do my engine work. If it's not right they can fix it.
I mill too much off or do a crummy job, I can't fix it. There is a lot to say about having the right tools to do the job and with somebody who knows how to do it.
11-20-2003, 11:05 PM
I had some four cylinder Onan heads That I couldn't get my local a guy to do,so what I did was make a face mill out of 1.5" thick plate and attached it(welded)to an old shell mill shank,it was 8" od when I got finished,I set it up in the mill and did the final turning with a toolbit clamped in the vise,I milled six slots around the edge and drilled and tapped for setscrews,mounted six c-5 brazed points and preset them with a gage block,I set up the head with a height gage to make sure it was parallel to the table,cranked it up and ghosted over for the first pass,turned the coolant on and made a single pass .035"deep with a .008-010"per rev feed rate,the result-perfect,I had no problem with the interuppted cut becuase the cutter was so massive.
I have seen heads ground too,one of the local shops uses a big belt sander type machine,total junk,there is no coolant on the machine so what happens is the bottom of the head heats up and warps upward as it expands,by then the head has been cut flat,but as the head cools and the expansion goes away the head warps in the other direction and is no longer flat.
One other tip I might add is that I have started taking things like valve covers,oil sumps and the casting faces they mate too and sandblasting the mating surfaces with a coarse sand,this leaves a uniform rough surface that with modern adhesives really holds a gasket good.
11-21-2003, 09:30 PM
At risk of getting OT here, I don't think you can say that unleaded fuel will necessarily give valve seat problems.
I know of two SB chevs which have both done high mileage with no problems and the valves seat directly into the heads.
The first has run on LPG since the 1980's, the second, my own 327, ran 195,000 miles in my ownership, the latter 100,000 miles (approx.) on unleaded. I rebuilt both these motors when first purchased, and have never touched them since.
When NZ went over to unleaded in the early 1990's, there was alot of worry, and it was common to put in a "squirt" at each fill-up (some kind of additive to lubricate valves), however, I knew this was not needed, because many vehicles had been running sucessfully on CNG and LPG for the previous ten years or so.
I know this is just my experience, but it shows me that it is simply not true that unleaded = problems in all engines without hardened valve seats.